The conventional direct-lit backlight module used for a display comprises LEDs directly disposed under the display panel. To enhance the uniformity, usually a diffuser plate or an optical lens being disposed in front of the LEDs is needed. Although the direct-lit backlight module is suitable for the large-scale displays, it can be well imagined that the direct-lit backlight module is too costly to add optical lens to each individual LED light sources but also too thick since a certain distance is needed for the diffuser plate to be disposed above the light sources in order to obtain an uniform light output over a large area. In other words, the direct-lit backlight module faces a dilemma to provide a uniform brightness or a thinner configuration.
Given the above, a lighting device being slim and providing uniform backlight is needed.